Volt problem while car is off

gmc
sonoma

#1

When I put the key in the volt meter reads about 9v and it’s hard to start but once I get it started it jumps up to 14v I can put a volt meter on the battery and it reads about the same. As soon as I turn the car off the batterys volts slowly goes down. It’s like something is on and drawing power. I have a new battery and had the battery and alternator checked. Both good. I have no idea what’s going on.


#2

I would appreciate any help. I have no clue what I’d going on. It’s like something is on and drawing power when the car is off. No one seems to know what is going on. Thank you everyone.


#3

Something is drawing power with the key off. Common culprits are radios (especially aftermarket), radar detectors, aftermarket alarm systems, anything that plugs into the OBD port (“safe driving discount” devices from your insurance company, etc), cell phones left on the charger, and lights.

The latter is fairly easy to trace. Park the car at night, turn it off, and get out. Look carefully for anything that’s emitting light, both inside and out. If the door sensor fails to notice that you closed the door, the dome light will stay on. If the brake light switch is out of alignment, the brake lights will stay on.

If you’ve eliminated all the easy stuff, then it’s time to start pulling fuses. You’ll want someone experienced in electrical diagnosis to help you with this. You’ll pull fuses and measure the current draw from the battery. When the drain stops, you’ve found the fuse that’s on the circuit which connects to the culprit device.


#4

I wonder if the problem might be the battery. I bought a brand new battery and had trouble starting the car. When I measured the voltage at the battery, it was 9 volts when the engine was not running and over 14 volts with the engine running. I disconnected the negative battery cable and hooked up my battery charger to the battery and charged it up overnight. The next morning I disconnected the battery charger and the voltage reading was about 12.6. I let the car sit for a couple of hours with the negative terminal disconnected and measured the battery voltage again. It was down to 9 volts. The battery had an internal short.


#5

you say you have a new battery in. How new? What was wrong with the old one? Was the vehicle doing the same thing with the old battery? Or is this a recent development?


#6

Good advice above. As mentioned the new battery could still be no good. There’s 6 cells I think so each cell must yield 2 volts for a total of 12 volts if everything is working. If you have just on one faulty cell you’d be down to 10 volts, and with some self discharging going on, 9 volts. If that was the problem you could remove the battery from the car, charge it up using a battery charger like Tridaq did, and test if it holds the 12 volt charge while it sits on the garage floor overnight. If it does, then you may have a current drain. Shops have a simple test to check for that. If you have experience using an amp meter, someone here can guide you through how that test is done. It’s not something that the typical diy’er would attempt tho.


#7

It’s not 12 volts it’s 12.6 because each cell is 2.1 volts.

If the battery is

12.5 = 85% charged
12.4 = 65%
12.3 = 50%
12.2 = 35%
12.1 = drained

Read more: http://www.city-data.com/forum/automotive/2008906-what-proper-voltage-fully-charged-car.html#ixzz4mlxbxJ9Q


#8

Nothing is on when the key is out. The only thing is the charging port can charge when the car is off but nothing was pluged in. I disconnected the charging port, turned off the aftermarket radio, pulled the fuse from the amp, tested the alternator (its good) and no luck. I think you are all right about the battery not being good. I bought a yellow top last month then realized it was 4yrs old. I have tried so many things, that has to be it. I will take it back tomorrow and let you know what happens. Thank you all so much for your expert knowledge :heart:


#10

That might be what you think, but there may be something that has failed and IS indeed drawing current. That was the last paragraph of @shadowfax 's post. If there is a short in the radio, it can draw current even with the car and the radio off. That said, pulling a car battery down to 9 volts takes a BIG current draw so I agree with the others who think its a battery. You likely have 2 cells shorted together.


#11

Reading 9 volts on the battery and still able to start the car, indicates a damaged battery.

For a good battery to read that low, it has to be 99% discharged and would not have enough energy to turn the starter.

I’d say you have 1 or 2 bad cells. The remaining cells somehow can deliver enough to turn the starter slowly…